Department of Statistics, University of Oxford, Oxford OX1 3TG, United Kingdom
Manuscript received December 10, 2001
Accepted for publication June 12, 2002
ABSTRACT
We analyze patterns of nucleotide variability at 15 X-linked loci and 14 autosomal loci from a North
American population of Drosophila simulans. We show that there is significantly more linkage disequilibrium
on the X chromosome than on chromosome arm 3R and much more linkage disequilibrium on both
chromosomes than expected from estimates of recombination rates, mutation rates, and levels of diversity.
To explore what types of evolutionary models might explain this observation, we examine a model of
recurrent, nonoverlapping selective sweeps and a model of a recent drastic bottleneck (e.g., founder event)
in the demographic history of North American populations of D. simulans. The simple sweep model is